The present invention relates to techniques for correcting for the effects of phase and amplitude offsets in radio devices that employ multiple-input multiple-output (MIMO) radio communication.
MIMO radio communication involves simultaneously transmitting a plurality of signals from a first device via corresponding ones of a plurality of antennas and receiving a plurality of signals at a plurality of antennas of a second device. Each device has a plurality of transmitters to upconvert the signals to be transmitted, and a plurality of receivers to downconvert the signals received at each of the plurality of antennas.
Many MIMO signal processing algorithms are known in the art. There are some MIMO radio algorithms that use information about the radio channel between the two devices to maximize the received signal-to-noise ratio (SNR) at each device. These MIMO radio algorithms rely on channel symmetry of the link between the two devices. Examples of MIMO radio algorithms that rely on channel symmetry are disclosed in, for example, commonly assigned U.S. patent application Ser. No. 10/174,728, filed Jun. 19, 2002, entitled “System and Method for Antenna Diversity Using Joint Maximal Ratio Combining,” U.S. patent application Ser. No. 10/174,689 filed Jun. 19, 2002, entitled “System and Method for Antenna Diversity Using Equal Power Joint Maximal Ratio Combining,” and U.S. patent application Ser. No. 10/064,482 filed Jul. 18, 2002, entitled “System and Method for Joint Maximal Ratio Combining Using Time-Domain Signal Processing.” These algorithms substantially increase the received signal-to-noise ratio, and in so doing, extend the range at which devices can communicate with each other.
Channel symmetry is lost if the transmitter and receiver paths of one device on the link are not identical, which degrades the performance of the MIMO radio algorithm. Mismatches in amplitude (gain) and phase responses between the data converters and antennas in each antenna path of a device due to analog circuit non-idealities in the transmitter and receiver for each antenna path may cause the channel response to become asymmetrical.
In order to fully exploit the benefits of MIMO radio algorithms that depend on channel symmetry in the link between the two devices, techniques are needed for correcting for amplitude and phase mismatches in each device on the MIMO radio link. These techniques are also useful when one device on the link has a MIMO radio and the other device has a single antenna or switched diversity antenna system.